Kids ask astronauts the questions adults are too polite to ask. So when YouTuber and former NASA engineer Mark Rober joined an Earth-to-space call with the International Space Station this week, one of them came up: what happens when you fart in space?
NASA astronaut Anil Menon, who’s been on the station since July, took it in stride. He even called himself an expert. His answer, reported by UNILAD Tech, is funny, but it also opens a window into one of the most important and least glamorous systems on the station: the one that keeps the air breathable.
The short version
- Without gravity, gas doesn’t rise or drift away. It hangs where it was released.
- Fans constantly move air through the ISS, so a fart gets passed from crew quarter to crew quarter, Menon says.
- The smell is temporary because filters and a hot catalytic reactor pull the gases out of the air.
- Early NASA engineers worried flammable gases like hydrogen and methane could build up. On the ISS, levels are far too low to matter.
- A spacesuit is a different story: there, the smell sticks around until the suit’s scrubbers clear it.
What Menon actually said
The call took place on November 4, streamed on NASA’s YouTube channel ahead of National STEM Day. Students asked about living in microgravity, and Menon showed off what ketchup and mustard do when they float. Then came the important question, which Rober joked kids would need answered before deciding to become astronauts.
“If there was no air circulation in space, it just kind of hangs there,” Menon said. “So I don’t know if it’d be forever, but it would probably last a long, long time.”
Luckily, the ISS has plenty of air circulation. “Our crew quarters, you’d be interested to know, have a fan that goes from one to the next to the next to the next, and it’s blowing the air between them,” he explained. “The idea is to just circulate oxygen, but it also, as a byproduct, circulates farts around.”
Asked whether the smell lingers, he gave credit to the people on the ground. “You only smell those farts temporarily on station because the good engineers at NASA put those filters in to catch all those particles or whatever creates the smell.”
Why gas just hangs there in space
On Earth, you rarely think about air moving. Warm air rises, cool air sinks, and that constant convection mixes everything. In microgravity, there’s no “up” for warm air to rise toward, so convection basically stops. Whatever you breathe out, or let out, stays in a cloud around you unless something pushes it away.
That’s not just an awkward social problem. It’s a safety one. Astronauts sleeping in a still pocket of air can end up rebreathing their own exhaled carbon dioxide, which causes headaches and worse. That’s why every crew quarter on the ISS has its own fan, and why the station hums with ventilation 24 hours a day. Moving farts around is an unintended side effect of a system that exists to keep people alive.
Where the gas actually goes
The ISS cleans its air with the Environmental Control and Life Support System, or ECLSS. One part of it, called the Trace Contaminant Control system, is what eventually deals with a fart. According to NASA technical papers, it uses three stages: an activated charcoal bed, a high-temperature catalytic oxidizer and a final sorbent bed.
The charcoal handles the heavier compounds, including many of the ones responsible for bad smells. The lighter gases charcoal can’t hold, such as methane, hydrogen and carbon monoxide, go through the catalytic oxidizer. NASA papers note that oxidizing methane takes temperatures of around 400°C (about 750°F), which turns it into carbon dioxide and water. The CO2 is then handled by the station’s separate carbon dioxide removal system.
There’s a fun twist buried in those engineering reports, too. NASA has found that hydrogen sulfide, the rotten-egg gas behind the worst smells, can permanently “poison” the catalyst that burns off methane. In other words, the smelliest part of a fart is also the part most likely to wear down the system that cleans it up. That’s one reason the charcoal bed sits in front of the oxidizer.
What’s actually in a fart
Most of a fart doesn’t smell at all. The odor comes from tiny traces of sulfur compounds. The rest is a mix of gases, some of which are flammable, which is exactly what worried early spaceflight engineers.
NASA once took this very seriously
In the 1960s, NASA genuinely worried that hydrogen and methane could build up inside small, oxygen-rich capsules and become a fire risk. The agency funded diet research to find out which foods made astronauts gassier. The answer won’t surprise anyone: beans were a problem, and menus were planned with that in mind.
Apollo astronauts had their own complaints. On Apollo 16 in 1972, John Young was caught on an open mic grumbling to Charlie Duke that he had the farts again, blaming the potassium-fortified orange juice they’d been given. The quote has been a NASA history favorite ever since.
The worry eased as spacecraft got bigger and air systems got better. On today’s ISS, the concentrations are far too low to be a toxic or fire hazard, and the station is huge compared to an Apollo capsule. Microgravity can still make astronauts gassier, though, since fluids shift around the body and swallowed air doesn’t separate from food the way it does on Earth.
| Where it happens | What happens to the gas | How long it lingers |
|---|---|---|
| On Earth | Convection and drafts spread and dilute it | Seconds to minutes |
| ISS, no fans | Hangs around the person who released it | “A long, long time,” per Menon |
| ISS, normal operation | Fans move it to filters and the catalytic oxidizer | Briefly smelled, then removed |
| Inside a spacesuit | Trapped by the base layer, then cycled through CO2 scrubbers | Until the suit’s filters clear it |
Spacesuits are the worst place for it
If the ISS is a big, well-ventilated house, a spacesuit is a sealed sleeping bag. Gas released inside one is trapped against the astronaut by the suit’s base layer and has to work its way through the carbon dioxide scrubbers before the air clears. Spacewalks can last more than six hours, so it’s easy to see why astronauts keep an eye on what they eat beforehand.
A question with a deadline
The ISS is in its final years. The first module launched in November 1998, crews have lived aboard continuously since November 2, 2000, and NASA plans to bring it down around 2030 using a SpaceX-built deorbit vehicle. Russian cosmonauts Oleg Kononenko and Nikolai Chub spent a record 374 consecutive days aboard in 2023 and 2024, which means a lot of hours testing that air system. When old spacecraft come home, they don’t always go quietly, as we saw when NASA’s Swift telescope fell back to Earth this week.
Space is full of strange practical problems, from bodily functions to orbital politics. If you’re curious about the bigger picture, an ex-NASA astronaut recently laid out what’s already in orbit and why he won’t rule out war in space.
Sources and further reading
- UNILAD Tech: NASA astronaut reveals what happens when someone farts on the ISS
- NASA: NASA Astronaut, STEM Creator Connect with Students for STEM Day
- YouTube: Astronaut Anil Menon Speaks With Mark Rober From the International Space Station
- NASA Technical Reports Server: ISS Trace Contaminant Control system
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